The document discusses the evolution of application logging practices, detailing incremental improvements since 2008 to capture significant logging data from multiple machines using Log::Log4perl and a centralized ELK stack (Elasticsearch, Logstash, Kibana). Key components include capturing warnings and fatal exceptions, managing logs per application, and integrating logs with external systems through rsyslog and haproxy for enriched context. The ultimate goal is to streamline log monitoring and enhance visibility across systems, aiding in troubleshooting and incident response.

1. Application Logging in
the 21st Century
Austrian Perl Workshop – Oct 2014
1

2. Logging is Like Lego
Many
Interchangeable
Options
Not the focus of this talk
2

3. Our Journey
• Almost no logging when I joined in 2008
• Incremental improvements as a background
project over years
• Currently capturing 600-900 logs / minute
from ~200 machines
• Not claiming "best practice", just some
hopefully useful tips from our long journey
3

4. Log file per-application
• Adopted Log::Log4perl
• Wrote utility function to add a log file
• Intercept warnings and fatal exceptions
• Simple layout with timestamp and severity
4

5. Log4perl Layout
Config file
log4perl.rootLogger = INFO, TLScreen
!
log4perl.appender.TLScreen = Log::Log4perl::Appender::Screen
log4perl.appender.TLScreen.layout = Log::Log4perl::Layout::PatternLayout
log4perl.appender.TLScreen.layout.ConversionPattern
= %d{yyMMdd HH:mm:ss} %.1p> %m{chomp} [@%F{1}:%L %M{1}()}]%n
Example output
140929 14:06:25 I> some info message [@Broker.pm:221 process()]
140929 14:06:27 W> a warning [@BlackOakClientRole.pm:296 get_runner_for_class()]
5

6. Capture Warnings
$SIG{__WARN__} = sub {
!
# protect against infinite recursion
return warn @_ ## no critic (RequireCarping)
if $within_log_sig
or not defined $Log::Log4perl::Logger::ROOT_LOGGER;
local $within_log_sig = 1;
!
local $Log::Log4perl::caller_depth = $Log::Log4perl::caller_depth + 1;
!
chomp(my $msg = shift);
get_logger()->warn($msg);
};
6

7. Capture Fatal Exceptions
$SIG{__DIE__} = sub {
!
return if $^S; # We're in an eval, so ignore it
die @_ if not defined $^S; # Parsing module/eval
!
# protect against infinite recursion
die @_ ## no critic (RequireCarping)
if $within_log_sig
or not defined $Log::Log4perl::Logger::ROOT_LOGGER;
local $within_log_sig=1;
!
local $Log::Log4perl::caller_depth = $Log::Log4perl::caller_depth + 1;
!
chomp(my $msg = shift);
get_logger()->fatal($msg);
die "$msgn"; # may duplicate message but that's better than loosing it
};
!
7

8. Were there any errors?
log4perl.rootLogger = INFO, TLScreen, TLErrorBuffer
!!
log4perl.appender.TLErrorBuffer = TigerLead::Log::Appender::RecentSummaryBuffer
log4perl.appender.TLErrorBuffer.Threshold = ERROR
log4perl.appender.TLErrorBuffer.max_messages = 10
log4perl.appender.TLErrorBuffer.layout = Log::Log4perl::Layout::PatternLayout
log4perl.appender.TLErrorBuffer.layout.ConversionPattern = %m{chomp}
!!
Ring buffer for log messages.
Used at the end of old batch job code to decide if something went wrong.
8

9. State of play
• Timestamped log message with severity etc
• Per-app log files
• Can tell if warnings or errors were produced
But:
• Not capturing stdout/stderr & non-perl apps
9

10. App s
Flow of log messages
X
10

11. AAppppss
Floiglses
Flow of log messages
X
11

12. Capturing stdout/stderr
setsid $start_daemons_command 2>&1
| setsid $capture_logs_command &
!
setsid puts deamons into a separate process group, isolated from terminal.
Capture stdout/stderr from all child processes and pipe to logger process.
Logger process is also in a separate isolated process group
We use daemontools so for us:
start_daemons_command="svscan $supervise_dir"
capture_logs_command="multilog t s1000000 n100 dir $logdir"
multilog t prepends high-resolution timestamps to log messages
multilog t accuracy depends on when the log was flushed
multilog s1000000 n100 dir does log rotation for us
Logger exits only when all child processes have closed stdout/stderr
even if they've become daemons, forked more child processes and died.
12

13. AAppppss common
Floiglses
Flow of log messages
13

14. State of play
• Capturing stdout/stderr & non-perl apps
But:
• We had to login to see what was happening
• No single place to watch errors and
warnings across the systems
• Wanted to parse log messages to extract
more useful info
14

15. Log Stream-Store-View
Stream:
Logstash – collect, edit, and forward logs
Store:
Elasticsearch – real-time distributed search
and analytics engine. JSON REST over Lucene
View:
Kibana – browser based analytics and search
dashboard for Elasticsearch
15

16. Logstash Stream Processing
Inputs: collectd drupal_dblog elasticsearch eventlog exec file ganglia gelf gemfire generator graphite heroku imap
invalid_input irc jmx log4j lumberjack pipe puppet_facter rabbitmq rackspace redis relp s3 snmptrap sqlite sqs stdin
stomp syslog tcp twitter udp unix varnishlog websocket wmi xmpp zenoss zeromq
Codecs: cloudtrail collectd compress_spooler dots edn edn_lines fluent graphite json json_lines json_spooler
line msgpack multiline netflow noop oldlogstashjson plain rubydebug spool
Filters: advisor alter anonymize checksum cidr cipher clone collate csv date dns drop elapsed elasticsearch
environment extractnumbers fingerprint gelfify geoip grep grok grokdiscovery i18n json json_encode kv metaevent
metrics multiline mutate noop prune punct railsparallelrequest range ruby sleep split sumnumbers syslog_pri throttle
translate unique urldecode useragent uuid wms wmts xml zeromq
Outputs: boundary circonus cloudwatch csv datadog datadog_metrics elasticsearch elasticsearch_http elasticsearch_river
email exec file ganglia gelf gemfire google_bigquery google_cloud_storage graphite graphtastic hipchat http irc jira juggernaut librato
loggly lumberjack metriccatcher mongodb nagios nagios_nsca null opentsdb pagerduty pipe rabbitmq rackspace redis redmine riak
riemann s3 sns solr_http sqs statsd stdout stomp syslog tcp udp websocket xmpp zabbix zeromq
16

17. Logstash Configuration
input {
stdin { }
}
!
filter {
grok {
match => { "message" => "%{COMBINEDAPACHELOG}" }
}
date {
match => [ "timestamp" , "dd/MMM/yyyy:HH:mm:ss Z" ]
}
}
!
output {
elasticsearch { host => localhost }
stdout { codec => rubydebug }
}
17

18. Elasticsearch Buzzwords
• Document oriented. Schema free.
• JSON in and out. RESTful API.
• Powerful indexing and search via Lucene.
• Distributed and massively scalable.
• Big community, rapid growth.
• Generally awesome.
18

19. Kibana
19

20. Our ELK setup
• Started with single machine
• Now using three machines
• Logstash, Elasticsearch and Kibana on each
• Elasticsearch cluster across all three
• HAProxy load balancer in front of all three
20

21. AAppppss common
logstash
ES
Kibana
Ffilielses
Flow of log messages
21

22. syslog forwarding
• Forwarding system syslog was easy first step
• We're using CentOS6 with rsyslog v7.6
• Started forwarding notice+ severity messages
but now forward info+
22

23. Rsyslog forwarding
# buffering config
$WorkDirectory /var/lib/rsyslog # where to place spool files
$ActionQueueFileName logstash # unique name prefix for spool files
$ActionQueueMaxDiskSpace 1g # 1gb space limit
$ActionQueueSaveOnShutdown on # save messages to disk on shutdown
$ActionQueueType LinkedList # run asynchronously
$ActionResumeRetryCount -1 # infinite retries if host is down
!!
# forward info+ level logs from all facilities to logstash
*.info @@logstash-app-stag.tigerlead.local:5544; RSYSLOG_ForwardFormat
!!
# RSYSLOG_ForwardFormat gives us high-resolution timestamp and timezone
# We use TCP (not UDP) for reliability may switch to RELP later
23

24. AAppppss common
logstash
ES
Kibana
System rsyslog
queue
Ffilielses
Flow of log messages
24

25. 25

26. Ship our logs to logstash
• Wanted to parse messages but didn't want
to do that on the central logstash server
• Started with a Message::Passing utility to tail
and parse specific logs files and ship as JSON
• Turned out we don't need much parsing
• Now using an extra rsyslogd that follows log
files and forwards to the local root rsyslogd
26

27. AAppppss common
Shipper logstash
ES
Kibana
System rsyslog
queue
Ffilielses
Flow of log messages
27

28. AAppppss common
rsyslog logstash
ES
Kibana
System rsyslog
queue
Ffilielses
Flow of log messages
28

29. Eradicating 'our' log files
• Still have our 'app log files' separate from the
'system log files' in /var/log/*
• Harder to correlate events between them
• Experiment: use syslog for more/everything?
• Want: per-app log files, high-res timestamp
with lexical ordering (sort -m *.log | ...)
• Let the system look after log rotation etc
29

30. Send app logs to syslog
log4perl.rootLogger = INFO, TLScreen, TLErrorBuffer, TLSyslog
!
log4perl.appender.TLSyslog = TigerLead::Log::Appender::Syslog
log4perl.appender.TLSyslog.layout = Log::Log4perl::Layout::PatternLayout
log4perl.appender.TLSyslog.layout.ConversionPattern = %m{chomp} [@%F{1}:%L %M{1}
()}]%n
!
The syslog format provides program name, severity and pid.
30

31. Eradicating 'our' log files
template( name="sortable_log_format" type="string" # format for log lines
# e.g. "2014-06-28 17:47:11.636078 $facility.$severity $program: $message"
string="%TIMESTAMP:::date-pgsql%.%TIMESTAMP:::date-subseconds% %PRI-TEXT%
%syslogtag%%msg:::sp-if-no-1st-sp%%msg:::drop-last-lf%n"
)
!
template( name="file_per_programname" type="string" # format for log file names
# e.g. program="run-parts(/etc/cron.hourly)"
# becomes "/var/log/tiger/run-parts" using the 'leading safe characters'
string="/var/log/tiger/%programname:R,ERE,0,ZERO:^[-_a-zA-Z0-9]+--end%.log"
)
!
ruleset(name="write_tiger_progname_log_files") {
action( Type="omfile" Template="sortable_log_format"
DynaFile="file_per_programname")
}
!
if ( ($syslogseverity <= 5) or not ($programname == [ ... ]) ) then {
call write_tiger_progname_log_files
}
31

32. Flow of log messages
AAppppss common
rsyslog logstash
ES
Kibana
Ffilielses
System rsyslog
Ffilielses queue
32

33. Logstash Enrichment #1
hostgroup - first word of server name
• handy to focus in on a group of servers
related to a particular service
punct - just the punctuation chars
• handy to focus on, or exclude, a particular
'shape' of message
33

34. Quick Demo
• Overview
• Drill-down
• Time ranges
• Multiple queries
• Share URL
34

35. State of play
• No longer had to login to multiple machines
to see what was happening
• Can easily drill-down to explore the logs
from multiple machines and systems
• Can share a URL to that view - very handy
But now:
• Want to be able to live-stream errors
35

36. Live-stream to IRC
• Separate production and staging channels
• Currently just error severity or higher
• Messages with 'alert' or 'emergency' severity
are also sent to main developer channel
• Proven to be very useful
36

37. Live-stream to IRC
But:
• occasionally have floods of messages
• logstash irc rate limiting behaviour is dumb
• want to rate-limit only 'repeated' messages
• 'repeated' should allow for minor differences
• logstash can help...
37

38. Enrichment: message_gist
mutate {
add_field => [ "message_gist", "%{message}" ] # copy to edit
}
mutate {
# normalize numbers
gsub =>[ "message_gist", "[-+]?[0-9]*.?[0-9]+([eE][-+]?[0-9]+)?", "N" ]
# normalize double quoted strings
gsub =>[ "message_gist", ""[^"]*"", "S" ]
# normalize single quoted strings, but try to avoid matching apostrophes
gsub =>[ "message_gist", "(A|W)'[^']*'(?!w)", "1S" ]
# truncate urls to remove the query/fragment part
gsub =>[ "message_gist", "(w:/[^?#s]*)S*", "1" ]
}
fingerprint { # convert the normalized string into an integer hash
source => "message_gist"
target => "message_gist"
method => "MURMUR3"
}
38

39. Enrichment: repeat tag
if [severity] and [severity] =~ /0|1|2|3|4/ {
!
throttle {
period => 60 # seconds
!
before_count => -1
after_count => 2 # allow N within period before throttling
!
key => "%{hostgroup}%{severity}%{program}%{message_gist}"
max_counters => 10000 # track this many variants
!
add_tag => "repeat"
}
!
# may add a more strict 'duplicate' tag here in future
# using period=>5, after_count=>1, and %{message} not %{message_gist}
}
39

40. Enrichment: late tag
# flooding may cause a backlog that delays messages reaching logstash
# tag messages that arrive 'late'
ruby {
code => "
msg_age = Time.now - event['@timestamp']
!
if msg_age >= +60 then msg_tag = 'late' # delayed
elsif msg_age <= -60 then msg_tag = 'early' # craziness
end
!
if msg_tag
then
event.tag msg_tag
event['message_delay'] = msg_age.to_i # age
end
"
}
40

41. Better IRC live-stream
if [severity] and [severity] =~ /0|1|2|3|4/
and "repeat" not in [tags]
and (![message_delay] or [message_delay] < 600) # not too 'late'
{
if [severity] =~ /0|1|2|3/ { # 4 (warning) is currently too noisy
irc {
channels => [ "#logprod" ]
messages_per_second => 10
format => "%{severity_label} %{host} %{program}: %{message}"
}
}
if [severity] =~ /0|1/ { # emergency and alert only
irc {
channels => [ "#l2dev" ]
messages_per_second => 5
format => "%{severity_label} %{host} %{program}: %{message}"
}
}
}
41

42. Flow of log messages
AAppppss common
IRC
rsyslog logstash
ES
Kibana
Ffilielses
System rsyslog
Ffilielses queue
42

43. State of play
• Live-stream to IRC, promotes awareness
• Developers work to reduce spurious noise
But now we want more context:
• "what was the app working on when that
warning or error was triggered?"
• "what was the web request URL?"
or "what were the async job parameters?"
43

44. How to get context?
• Add more info into every log message text,
then parse it out again? Not ideal.
• Start by capturing all the HTTP access logs
• Could do log-shipping for each access log file
• But all traffic passes through HAProxy
• So HAProxy logging can give us everything
44

45. HAProxy logs
• already had haproxy notice+ messages
• now added haproxy traffic logs,
first HTTP then TCP as well
• can include one request and response cookie
• plus multiple request and response headers
45

46. HAProxy Configuration
defaults
mode tcp
log-format %ci [%t] %ft %b/%s %Tw/%Tc/%Tt %U %B %ts %ac/%fc/
%bc/%sc/%rc %sq/%bq
!
defaults
mode http
log-format %ci [%t] %ft %b/%s %Tw/%Tc/%Tt %U %B %tsc %ac/%fc/
%bc/%sc/%rc %sq/%bq %ID %{+Q}r %ST %Tq/%Tr %{+Q}CC %{+Q}hr %{+Q}CS
%{+Q}hs
!
frontend stripes-prod-frontend 108.168.241.12:80 # example service
capture request header Referer len 200
capture request header User-agent len 300
capture response header Location len 300
capture cookie _session= len 63
46

47. HAProxy Logs
Example TCP log:
!
10.60.201.12 [09/Oct/2014:22:29:45.317] carbon-stag-frontend carbon-stag-backend/
carbon-app-stag-ddc-01 1/0/2 3040 0 -- 57/45/45/45/0 0/0
!
Example HTTP log:
!
10.60.199.78 [09/Oct/2014:21:34:04.361] apex-fe-stag-frontend apex-fe-stag-backend/
apex-fe-stag-ddc-01 0/0/2594 956 86661 ---- 63/1/0/0/0 0/0
0A3CC74E:CC62_0A3CC933:0050_5436FF4C_462C7E:696C "GET /a/sa/search?
rgu=0&domain_id=10366 HTTP/1.1" 200 337/2256
"_session=4889b2859286db6511f2e9e9b33cdbe37f5b43ab" "{|Mozilla/5.0 (Windows
NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.124
Safari/537.36}" "f_session=4889b2859286db6511f2e9e9b33cdbe37f5b43ab" "{}"
47

48. Logstash for HAProxy
• change the host field (and thus hostgroup) to
the backend machine name, so the logs from
haproxy appear to be coming from the
appropriate machine
• parse out request URL parameters
• decode URL parameters
48

49. Logstash for HAProxy
# extract the request url params into a 'params' hash
mutate { gsub => [ "request", "#.*", "" ] } # remove fragment, if any, first
kv { source => "request" field_split => "&?" target => "params" }
!
# XXX disabled re https://github.com/elasticsearch/logstash/issues/1695
# urldecode { field => "params" all_fields => true }
!
if [response] >= 500 {
mutate { replace => [ "severity", "4", "severity_label", "warn" ] }
}
else if [response] >= 400 {
mutate { replace => [ "severity", "5", "severity_label", "notice" ] }
}
!
mutate { # replace raw message with a human friendly version to view/search on
gsub => [ "request", "?.*", "" ] # remove params now we've extracted them
replace => [ "message", "%{be_host} %{client_ip} %{Tw}/%{Tc}/%{Tt}ms %
{bytes_in}b %{bytes_out}b %{response} %{verb} %{request}" ]
}
(Abridged!)
49

50. State of play
• now have detailed TCP and HTTP traffic logs
But:
• still parsing textual messages
• still hard to handle multi-line messages
• still don't have contextual data for logs
• still can't correlate http to application logs
50

51. Log as JSON from app
• Parsing textual log messages to extract data
that your own code put there is a bit dumb
• Log as JSON lines instead (jsonlines.org)
• Opens the door to logging extra information
• Bonus: solves the multi-line message problem,
at least for perl apps
51

52. Log::Log4perl::Layout::JSON
log4perl.rootLogger = INFO, TLScreen, TLFile, TLErrorBuffer, TLSyslogJSON
!
log4perl.appender.TLSyslogJSON = TigerLead::Log::Appender::Syslog
log4perl.appender.TLSyslogJSON.Threshold = INFO
log4perl.appender.TLSyslogJSON.layout = Log::Log4perl::Layout::JSON
log4perl.appender.TLSyslogJSON.layout.prefix = @cee: # used as tag
log4perl.appender.TLSyslogJSON.layout.field.message = %m
log4perl.appender.TLSyslogJSON.layout.field.src_file = %F{1}
log4perl.appender.TLSyslogJSON.layout.field.src_sub = %M{1}
log4perl.appender.TLSyslogJSON.layout.field.src_line = %L
!
Example output (spaces and line breaks added for clarity):
!
2014-10-08 12:56:28.641086 local0.info 70-lead-basic-t[13374]: @cee:{
"message":"...n...n...", "src_file":"Foo.pm", "src_sub":"frobnicate",
"src_line":"18" }
!
Note that src_file, src_sub and src_line used to be appended to the message text.
52

53. Decoding JSON in logstash
grok {
# @cee: is syslog 'CEE Event Flag' per https://cee.mitre.org/
match => { message => "^@cee: ?%{GREEDYDATA:cee_data}" }
add_tag => [ "cee" ]
tag_on_failure => []
}
!
if ("cee" in [tags]) {
json {
source => "cee_data"
remove_field => [ "cee_data" ]
}
}
53

54. State of play
• now have rich JSON formatted log messages
• multi-line messages are no longer a problem
But:
• still only very basic contextual data for logs
• still can't correlate http to application logs
54

55. "Context Data"
• Significant items of 'ambient information'
• The current 'things being worked on'
• Would like that info added to any log msgs
• Including warnings and fatal exceptions
(e.g. if hooked via $SIG{__WARN__})
55

56. Context Data
for my $foo_id (@list_of_foo_ids) {
!
# we want the current $foo_id value to be included
# in any log messages in this scope
!
do_something_useful($foo_id);
}
!
# we DON'T want $foo_id to be included in any future log messages
56

57. Context Data
• Put the 'ambient information' in a hash
• Add the contents of the hash to the JSON
• Use local to limit the scope
57

58. Context Data
for my $foo_id (@list_of_foo_ids) {
local log_context->{foo_id} = $foo_id; # simple!
do_something_useful($foo_id);
}
The imported log_context utility:
sub log_context { return %Log::Log4perl::MDC::MDC_HASH }
The Log::Log4perl::Layout::JSON config line:
log4perl.appender.TLSyslogJSON.layout.include_mdc = 1
58

59. Context Data
Context added to root hash by default:
2014-10-08 12:56:28.641086 local0.info 70-lead-basic-t[13374]: @cee:{
"message":"...n...n...", "src_file":"Foo.pm", "src_sub":"frobnicate",
"src_line":"18", "foo_id":42 }
Optionally put context data items into a nested hash:
log4perl.appender.TLSyslogJSON.layout.name_for_mdc = extra_stuff
!
2014-10-08 12:56:28.641086 local0.info 70-lead-basic-t[13374]: @cee:{
"message":"...n...n...", "src_file":"Foo.pm", "src_sub":"frobnicate",
"src_line":"18", "extra_stuff":{ "foo_id":42 } }
59

60. State of play
• now have easy way to add contextual data
• array and hash refs work (keep it small)
But:
• what contextual data should we include?
• request URL? decoded parameters?
• expensive to include in every message
60

61. HAProxy Correlation
• We have a stream of haproxy logs
• We have a stream of application logs
• Want to be able to correlate them
"what HTTP request caused this warning?"
• Add unique-id to HTTP log & HTTP header
61

62. HAProxy Configuration
defaults
mode http
unique-id-format %{+X}o %ci:%cp_%fi:%fp_%Ts_%rt:%pid
unique-id-header X-TLXID
log-format %ci [%t] %ft %b/%s %Tw/%Tc/%Tt %U %B %tsc %ac/%fc/
%bc/%sc/%rc %sq/%bq %ID %{+Q}r %ST %Tq/%Tr %{+Q}CC %{+Q}hr %{+Q}CS
%{+Q}hs
!
• HAProxy now generates a unique-id for each HTTP request
• Adds it to the HTTP request as a X-TLXID header
• Includes the unique-id value in the syslog message
62

63. Capture X-TLXID
package TigerLead::Plack::Middleware::SetUpLogContext;
use strict;
use warnings;
use parent qw( Plack::Middleware );
!
use Plack::Request;
use TigerLead::Log qw(log_context);
!
sub call {
my($self, $env) = @_;
!
my $req = Plack::Request->new($env);
# reset log context at start of a new request
%{log_context()} = (tlxid => scalar $req->header('X-TLXID'));
!
return $self->app->($env);
}
63

64. Correlation
• Given any log message from a web app we
can now find the HTTP request that was
being processed at the time
• That includes the session cookie, so we can
view the stream of requests for that session
• Demo...
64

65. Questions?
65